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package org.jooby.scanner;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
import com.google.common.util.concurrent.Service;
import com.google.common.util.concurrent.ServiceManager;
import com.google.inject.Binder;
import com.google.inject.Module;
import com.typesafe.config.Config;
import io.github.classgraph.ClassGraph;
import io.github.classgraph.ClassInfo;
import io.github.classgraph.ScanResult;
import org.jooby.Env;
import org.jooby.Jooby;
import org.jooby.Router;
import org.jooby.funzy.Throwing;

import static org.jooby.funzy.Throwing.throwingSupplier;

import org.jooby.mvc.Path;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.inject.Named;
import javax.inject.Provider;
import javax.inject.Singleton;
import java.lang.reflect.Modifier;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Optional;
import java.util.Set;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * <h1>scanner</h1>
 * <p>
 * Classpath scanning services via
 * <a href="https://github.com/lukehutch/fast-classpath-scanner">FastClasspathScanner</a>.
 * FastClasspathScanner is an uber-fast, ultra-lightweight classpath scanner for Java, Scala and
 * other JVM languages.
 * </p>
 *
 * <h2>usage</h2>
 *
 * <pre>{@code
 * {
 *   use(new Scanner());
 * }
 * }</pre>
 *
 * <p>
 * This modules scan the application class-path and automatically discover and register
 * <code>MVC routes/controllers</code> and {@link Jooby} applications.
 * </p>
 *
 * <p>
 * It scans the application package. That's the package where your bootstrap application belong to.
 * Multi-package scanning is available too:
 * </p>
 *
 * <pre>{@code
 * {
 *   use(new Scanner("foo", "bar"));
 * }
 * }</pre>
 *
 * <h2>services</h2>
 *
 * <p>
 * The next example scans and initialize any class in the application package annotated with
 * <code>Named</code>:
 * </p>
 *
 * <pre>{@code
 * {
 *   use(new Scanner()
 *     .scan(Named.class)
 *   );
 * }
 * }</pre>
 *
 * <p>
 * The next example scans and initialize any class in the application package that implements
 * <code>MyService</code>:
 * </p>
 *
 * <pre>{@code
 * {
 *   use(new Scanner()
 *     .scan(MyService.class)
 *   );
 * }
 * }</pre>
 *
 * <p>
 * Guava {@link Service} are also supported:
 * </p>
 *
 * <pre>{@code
 * {
 *   use(new Scanner()
 *     .scan(com.google.common.util.concurrent.Service.class)
 *   );
 *
 *   get("/guava", req -> {
 *     ServiceManager sm = req.require(ServiceManager.class);
 *     ...
 *   });
 * }
 * }</pre>
 *
 * <p>
 * They are added to {@link ServiceManager} and started and stopped automatically.
 * </p>
 *
 * <p>
 * Raw/plain Guice {@link Module} are supported too
 * </p>
 * :
 *
 * <pre>{@code
 * {
 *   use(new Scanner()
 *     .scan(Module.class)
 *   );
 * }
 * }</pre>
 *
 * <p>
 * Of course, you can combine two or more strategies:
 * </p>
 *
 * <pre>{@code
 * {
 *   use(new Scanner()
 *     .scan(MyService.class)
 *     .scan(Named.class)
 *     .scan(Singleton.class)
 *     .scan(MyAnnotation.class)
 *   );
 * }
 * }</pre>
 *
 * <p>
 * In all cases, services are created as <code>singleton</code> and started/stopped automatically
 * when {@link PostConstruct} and {@link PreDestroy} annotations are present.
 * </p>
 *
 * @author edgar
 * @since 1.0.0
 */
public class Scanner implements Jooby.Module {

  @SuppressWarnings("rawtypes")
  private static final Predicate<Class> A = Class::isAnnotation;

  @SuppressWarnings("rawtypes")
  private static final Predicate<Class> C = k -> !Modifier.isAbstract(k.getModifiers());

  @SuppressWarnings("rawtypes")
  private static final Predicate<Class> I = A.negate().and(Class::isInterface);

  @SuppressWarnings("rawtypes")
  private static final Predicate<Class> S = I.or(A).negate();

  private List<String> packages;

  @SuppressWarnings("rawtypes")
  private final Set<Class> serviceTypes = new LinkedHashSet<>();

  /**
   * Creates a new {@link Scanner} and uses the provided scan spec or packages.
   *
   * @param scanSpec Scan spec or packages. See <a href=
   *        "https://github.com/lukehutch/fast-classpath-scanner/wiki/2.-Constructor#specifying-more-complex-scanning-criteria">Scan
   *        spec</a>.
   */
  public Scanner(final String... scanSpec) {
    this.packages = Lists.newArrayList(scanSpec);
  }

  /**
   * Creates a new {@link Scanner} and use the application package (a.k.a as namespace).
   */
  public Scanner() {
  }

  @SuppressWarnings({"unchecked", "rawtypes"})
  @Override
  public void configure(final Env env, final Config conf, final Binder binder) {
    List<String> packages = Optional.ofNullable(this.packages)
        .orElseGet(() -> ImmutableList.of(conf.getString("application.ns")));
    Set<String> spec = Sets.newLinkedHashSet(packages);
    serviceTypes.forEach(it -> spec.add(it.getPackage().getName()));

    ClassGraph scanner = new ClassGraph().enableAllInfo()
        .whitelistPackages(spec.toArray(new String[spec.size()]));

    Router routes = env.router();

    ClassLoader loader = getClass().getClassLoader();
    Throwing.Function<String, Class> loadClass = loader::loadClass;

    // bind once as singleton + post/pre callbacks
    Set<Object> bindings = new HashSet<>();
    Predicate<Object> once = bindings::add;

    Consumer<Class> bind = klass -> {
      binder.bind(klass).asEagerSingleton();
      env.lifeCycle(klass);
    };

    ScanResult result = scanner.scan();

    Predicate<ClassInfo> inPackage = c -> packages.stream()
        .anyMatch(c.getName()::startsWith);

    /** Controllers: */
    result.getClassesWithAnnotation(Path.class.getName())
        .stream()
        .filter(once)
        .map(ClassInfo::getName)
        .map(loadClass)
        .filter(C)
        .forEach(routes::use);

    String mainClass = conf.getString("application.class");
    /** Apps: */
    result.getSubclasses(Jooby.class.getName())
        .stream()
        .filter(once)
        .map(ClassInfo::getName)
        .filter(name -> !name.equals(mainClass))
        .map(loadClass)
        .filter(C)
        .forEach(klass -> routes.use(((Jooby) newObject(klass))));

    /** Annotated with: */
    serviceTypes.stream()
        .filter(A)
        .forEach(a -> result.getClassesWithAnnotation(a.getName())
            .stream()
            .filter(once)
            .map(ClassInfo::getName)
            .map(loadClass)
            .filter(C)
            .forEach(bind));

    /** Implements: */
    serviceTypes.stream()
        .filter(I)
        .filter(type -> type != Jooby.Module.class && type != Module.class && type != Service.class)
        .forEach(i -> result.getClassesImplementing(i.getName())
            .stream()
            .filter(inPackage)
            .filter(once)
            .map(ClassInfo::getName)
            .map(loadClass)
            .filter(C)
            .forEach(bind));

    /** SubclassOf: */
    serviceTypes.stream()
        .filter(S)
        .forEach(k -> result.getSubclasses(k.getName())
            .stream()
            .filter(inPackage)
            .filter(once)
            .map(ClassInfo::getName)
            .map(loadClass)
            .filter(C)
            .forEach(bind));

    /** Guice modules: */
    if (serviceTypes.contains(Module.class)) {
      result.getClassesImplementing(Module.class.getName())
          .stream()
          .filter(inPackage)
          .filter(once)
          .map(ClassInfo::getName)
          .map(loadClass)
          .filter(C)
          .forEach(klass -> ((Module) newObject(klass)).configure(binder));
    }

    /** Guava services: */
    if (serviceTypes.contains(Service.class)) {
      Set<Class<Service>> guavaServices = new HashSet<>();
      result.getClassesImplementing(Service.class.getName())
          .stream()
          .filter(inPackage)
          .filter(once)
          .map(ClassInfo::getName)
          .map(loadClass)
          .filter(C)
          .forEach(guavaServices::add);

      if (guavaServices.size() > 0) {
        guavaServices(env, binder, guavaServices);
      }
    }
  }

  /**
   * Add a scan criteria like an annotation, interface or class.
   *
   * @param type A scan criteria/type.
   * @return This module.
   */
  public Scanner scan(final Class<?> type) {
    // standard vs guice annotations
    if (type == Named.class || type == com.google.inject.name.Named.class) {
      serviceTypes.add(Named.class);
      serviceTypes.add(com.google.inject.name.Named.class);
    } else if (type == Singleton.class || type == com.google.inject.Singleton.class) {
      serviceTypes.add(Singleton.class);
      serviceTypes.add(com.google.inject.Singleton.class);
    } else {
      serviceTypes.add(type);
    }
    return this;
  }

  private static <T> T newObject(final Class<T> klass) {
    return throwingSupplier(klass::newInstance).get();
  }

  @SuppressWarnings({"unchecked", "rawtypes"})
  private static void guavaServices(final Env env, final Binder binder,
      final Set<Class<Service>> serviceTypes) {
    Consumer<Class> guavaService = klass -> {
      binder.bind(klass).asEagerSingleton();
      serviceTypes.add(klass);
    };

    serviceTypes.forEach(guavaService);
    // lazy service manager
    AtomicReference<ServiceManager> sm = new AtomicReference<>();
    Provider<ServiceManager> smProvider = sm::get;
    binder.bind(ServiceManager.class).toProvider(smProvider);
    // ask Guice for services, create ServiceManager and start services
    env.onStart(r -> {
      List<Service> services = serviceTypes.stream()
          .map(r::require)
          .collect(Collectors.toList());
      sm.set(new ServiceManager(services));
      sm.get().startAsync().awaitHealthy();
    });
    // stop services
    env.onStop(() -> sm.get().stopAsync().awaitStopped());
  }

  @SuppressWarnings({"unchecked", "rawtypes"})
  private static Predicate<Class> type(final Class type) {
    return klass -> klass.isAssignableFrom(type);
  }

}
